A power generation unit generally consists of an electrical machine, such as a synchronous generator that is driven by a steam turbine, or other mechanical force-generating device, which is connected through a network of electrical transmission lines to various electrical loads that consume the generated power. To achieve such a result, a rotor maintained by the power generator is coupled to a rotating output shaft, or prime mover, that is driven by the steam turbine, resulting in the generation of electrical power. The generated power is delivered to a power transmission and distribution network, hereinafter referred to as a power delivery network, which supplies the generated power to various electrical loads. Thus, an integrated power system which combines the power generation unit with that of a transmission network, forms an electromechanical system, whereby the electromechanical oscillations that develop during the conversion of the mechanical energy supplied by the turbine into electrical power output by the generator are characterized by Newton's second law of motion in rotational form. As such, the power generation unit, which includes the power generator that performs the electromechanical conversion of the input mechanical power from a turbine shaft driving the rotor of the generator, is characterized by an inertia (mass) that is attributed to the generator's rotor, while the power delivery network can be viewed as a nonlinear spring. Thus, any mismatch between the mechanical power supplied by the prime mover to the generator, and the electrical power supplied by the power generator to the power delivery network results in the variable increase or decrease in the rotational speed of the prime mover. Such variability in the rotation of the prime mover is also characterized as electromechanical disturbances, or power oscillations that propagate throughout the integrated power system that includes the power generation unit and the power delivery network.
In general, electromechanical disturbances or oscillations imparted to power systems tend to degrade the overall quality of power supplied by the power generation system, and oftentimes compromises stability and reliability of the generation unit and the delivery network. Such oscillations also contribute to the unnecessary degradation of associated equipment and components that form the power generation unit and delivery network. Additionally, the oscillations may result in disruptive generator tripping, causing power outages, which are performed to protect the expensive components of the generator from exposure to the oscillations. To limit or reduce such oscillations, the integrated power system that incorporates the power generator and the delivery network has an inherent or natural damping characteristic associated with the physical electromechanical phenomena of the system. The degree of natural damping depends primarily on the particular manner of power generation, the electrical characteristics of the loads being powered, as well as the relative geographical position of the power generation system and associated loads. However, the degree of natural electromechanical damping is generally minimal for such an integrated power system, and thus in order to achieve acceptable damping performance that provides a suitable level of stabilization throughout the integrated power system, separate control systems, such as power system stabilizers (PSS), are installed to contribute additional levels of electromechanical damping to the power generator. In other words, supplemental control systems, in the form of power system stabilizers (PSS), are needed to ensure prompt elimination of oscillatory disturbances that are created by the power generation system, so as to prevent the degradation of the components of the power distribution and transmission system. Therefore, most transmission operators that oversee or manage the operation of the delivery network require installation of power system stabilizers (PSS) at the power generating units to improve the operational stability of the integrated power system to prevent the occurrence of such oscillatory events.
In particular, power system stabilizers (PSS) comprise a feedback controller that may be realized in software, hardware, or a combination of both, which provides a control input to an actuator maintained by the power generator. For example, in the case of a synchronous power generation unit, the actuator to which the control input is supplied comprises an automatic voltage regulator (AVR) and a field circuit that is associated with the power generator. By providing the appropriate control input to the AVR due to the operation of the PSS, the appropriate amount of damping is supplied in phase with the speed of the rotor of the power generator via the field circuit. And thus, the PSS is able to maintain suitable system stability before damage to the power generation unit or delivery network occurs.
Furthermore, the operation of the integrated power system to maximize power generation and transmission capacities, as well as the development of alternative techniques of power generation also creates conditions that are conducive for the generation of electromechanical oscillations. For example, next generation power generators are being designed with lower H-factors (megawatts per-unit megavolt-amp) to achieve more efficient operation, while the development of non-conventional energy generation methods, such as wind power generation, contribute to the increasing frequency and severity of such electromechanical oscillations. In addition, operating strategies to increase the use of existing power generation networks subjects such systems to more stress, and thus increases the frequency in which such systems are exposed to electromechanical oscillations that result after a fault condition in the electric delivery network has been encountered.
Thus, due to the continued growth in power consumption, power systems are likely to continue to be operated in a manner to maximize their power transmission throughput. Furthermore, new generator design reduces the stored kinetic energy maintained in the power generators and the associated turbines that drive them, thus resulting in more severe electromechanical oscillations. While, the unpredictable nature of the electromechanical outputs provided by alternative power generation systems, such as wind power, makes the management of electromechanical oscillations generated thereby a significant challenge.
In addition to the challenges in managing such electromechanical oscillations, the manner in which such oscillations are monitored and reported also present obstacles to those responsible for ensuring the integrity and stability of the power delivery network. For example, power generation utilities that manage the operation of the power generation unit, and power delivery utilities that manage the operation of the power delivery network typically comprise separate, unrelated entities that may have disparate operating agendas and protocols. As such, power delivery utilities rely on the operators of the power generation systems or power generation utilities to provide adequate electromechanical damping to the power generation systems, via the power system stabilizers (PSS) to prevent the degradation of the various components of the power delivery network, as well as to preserve or otherwise maintain the stability and integrity of the power delivery network. Unfortunately, due to the nature of the industry, power generation utilities often disable the power system stabilizers (PSS) that supply damping to the power generation systems. For example, the power system stabilizers (PSS) may be deactivated by the power generation utilities due to poor controller parameter design and settings. Alternatively, operators of the power generation systems may perform ad-hoc tuning of the PSS to find its gain, which may then be kept fixed for all operating points or power generation output levels or magnitudes. Thus, the chosen gains may cause the overall power generation and delivery system to be unstable when the generation system is operated at a power output level that is not complemented by appropriate levels of damping or may result in the decrease in the damping of the overall system, which makes the system more susceptible to electromechanical oscillations.
Furthermore, the power system stabilizers (PSS) may simply be disabled by those overseeing the operation of the power generation utilities due to poor tuning of the PSS. This may result in the generator oscillating against the power delivery system during what is thought to be “normal” operation of the power generators, which according to industry reports has occurred worldwide, including in India and Mexico. Unfortunately, the system operator or other supervising entity responsible for overseeing the operation of the power delivery utility has limited means to identify whether the power generating units are providing suitable levels of damping to effectively contribute to the dynamic stability of the power delivery system.
In addition to providing the appropriate amount of damping to the power generation system via the PSS, power generation utilities are required to report their PSS operation to various supervisory and regulatory bodies, such as the North American Electric Reliability Corporation (NERC), on a periodic basis to confirm their compliance with damping guidelines. In one implementation of the reporting process, power generation utilities with power system stabilizer (PSS) functionality are required to report the operating hours of the PSS on a quarterly basis, while hours of operation without PSS operation are required to be annotated with sufficient information regarding PSS outage, excitation system outage, generator maintenance, and the like.
Unfortunately however, a major drawback to such reporting efforts is that PSS reports themselves are susceptible to being readily altered, as there is generally no mechanism to verify the accuracy of the data contained in the report. Although, off-line PSS compliance monitoring systems, or systems whereby compliance is assessed during an analysis that is subsequent to the occurrence of an adverse oscillation, are available for use to determine accurate reporting of PSS operation is taking place, such monitoring systems are only triggered by large and/or irregular system disturbances, such as an electrical fault or change in the magnitude or other attribute of the loads being powered. Furthermore, such off-line analysis is time-consuming, and due to the nature of the operation of power delivery networks, is typically initiated after a significant amount of time, such as several weeks for example. Thus, such post-disturbance PSS analysis does not provide a proactive system that enables quick response to non-complying PSS operation, which would contribute to the improvement in power generation and delivery stability. Additionally, even after such post-disturbance PSS compliance analysis is performed by the power generating utility, the power delivery utility must rely on the premise that the power generating utility is reporting the results of its compliance analysis accurately.
Therefore, there is a need for a system to collect on-line (real-time) and/or off-line data to determine whether the power system stabilizers (PSS) maintained by a power generation unit are being operated in accordance with specific guidelines for electromechanical damping. Additionally, there is a need for a system that allows an individual to benchmark the actual and historical electromechanical damping values for subsequent comparison using statistical techniques. Furthermore, there is a need for an independent or autonomous system that is configured to be electrically coupled to a power delivery bus to collect on-line and/or off-line electromechanical damping data associated with a power generation unit.